The present invention relates to a liquid pressure regulator of the type that is used in liquid conducting systems such as irrigation equipment. The pressure regulator of the present invention maintains the pressure in the outlet of the regulator relatively constant, regardless of the pressure in the inlet.
The pressure regulator of the present invention is formed by a total of six pieces which include three main pieces and three accessories. The three main pieces include an inlet piece, an intermediate piece having a plunger which moves over a piston fixed to the previous piece, and an outlet piece which encloses the intermediate piece. The three accessories include a seal, a supportive element and a spring.
The pressure regulator of the present invention includes a double enclosing cone which makes it extremely effective. The regulator includes two or more supports between the plunger and the fixed piston which results in a coaxial sliding with respect to one another. The spaces formed between the front supports communicate with the atmosphere. These improvements ensure that the present invention is a simple pressure regulator with few and inexpensive pieces, but at the same time is highly effective.
The pressure regulators most frequently used today differ substantially from the present invention, as shown in the prior art regulators described in U.S. Pat. No. 4,543,985, U.S. Pat. No. 5,257,646 and U.S. Pat. No. 5,875,815. The technical differences between the prior art regulators and the present invention are primarily provided by the location where the regulation of the pressure is produced.
In the prior art regulators, the liquid enters through the center and is directed to the periphery by means of a deflector star which immediately diverts to the center where the regulation takes place. During the first step, the central flow moves to the periphery, and in the second step, this same flow moves from the periphery back to the center where the regulation takes place. However, these prior art regulators are significantly more complex than the present invention because they have, on average, a total of at least 18 components.
In the present invention, regulation takes place during the first step when the flow moves from the center to the periphery of the regulator. The flow moves back to the center only when leaving the device. This permits the present invention to be significantly less complicated and less costly than the prior art regulators while being highly effective and efficient.
Prior art regulators are disclosed in U.S. Pat. No. 4,474,207 and U.S. Pat. No. 2,888,033. The regulators of these patents are not frequently used today because they provide inaccurate pressure regulation due to the non-coaxial sliding of the intermediate cylindrical piece with respect to the inlet piece and due to the point of contact between the plunger and the inlet piece being flat on both pieces.
Another important factor affecting inaccuracy is that because there is a single supporting point between the plunger and the fixed piston, the axis of the plunger is unstable and, therefore, it does not move in a coaxial manner with respect to the fixed piston of the inlet piece. This produces lateral movements or inclination. Thus, the non-coaxial movement of the cylindrical piece produces a lack of accuracy of the regulator and a high level of hysteresis.
With respect to the lack of accuracy of this type of regulator, when the axis of the plunger does not have a coaxial and aligned position with respect to the axis of the piston, the closing of the plunger over the inlet piece is not consistent around the entire perimeter and, therefore, there are pressure leaks from the inlet to the outlet resulting in the regulator being inaccurate. Further, these differences are not constant, so for the same inlet pressure, there are different outlet pressures and, therefore, inaccuracy results.
With respect to hysteresis, hysteresis may be observed when the performance of the regulator is represented on a graph in which the x-axis is the inlet pressure of the regulator and the y-axis the outlet pressure of the regulator. Two curves are obtained as the inlet pressure is varied. One curve results from the increase of the inlet pressure while the other curve is obtained as this pressure decreases. The difference between these two curves is called hysteresis, as shown in Graph No. 1. The upper curve was obtained by increasing the pressure in the inlet of the regulator, while the lower curve was obtained while decreasing the pressure in the inlet of the regulator. All pressure regulators have hysteresis, but the lower the hysteresis, the more efficient the regulator will be.
However, when the movement between the plunger and the piston is not coaxial, it is difficult for the plunger to return to its original position, thus increasing the hysteresis of the regulator. To overcome these problems, U.S. Pat. No. 2,888,033 has a screw which fixes the position of the plunger, consequently causing an inclination of this piece from its initial position. Also, U.S. Pat. No. 4,474,207 discloses the use of additional ribs on the housing. These ribs should have very little space (almost none) over the plunger to be effective, a structure which increases the level of hysteresis. However, if a larger space is left to decrease the level of hysteresis, lateral movements cannot be avoided.
Also, the surfaces of contact between the plunger and the inlet piece of the present invention are flat. U.S. Pat. Nos. 4,474,207 and 2,888,033 share this structural characteristic. The problem of accuracy occurs when flow is low because there needs to be a small and accurate closing. In this operating condition, it is found that the change of pressure from the inlet to the outlet pressure does not occur in a single point. This change in pressure occurs throughout the thickness of the plunger. This means that there is an inlet pressure on one side of the plunger and an outlet pressure on the other. Consequently, if the closing is flat, the decrease of pressure from the inlet to the outlet is progressive throughout the length or thickness of that plane. This means that there is an intermediate pressure between the inlet pressure and the outlet pressure and, logically, this intermediate pressure is directly proportional to the inlet pressure because the higher the inlet pressure is, the higher the intermediate pressure will be.
It is important to consider that the surface of the plunger which produces the opposing force of the spring is its exterior surface, without considering the surface of the thickness, since this surface receives pressure from both sides. Because the surface of the thickness is below the intermediate pressure, which varies and is affected directly by the inlet pressure, the opposing force of the regulation spring decreases with the increase of the inlet pressure. Thus, theoretically, the outlet pressure on the other side of the plunger is constant. In this manner, the regulation is ineffective and increases the level of hysteresis. With high flow, where the closing should not be narrow, this effect is not very important, even though it exists. However, its presence with low flow is significant.
Another problem of the structure of U.S. Pat. No. 4,474,207 is that the teeth, which position the plunger, must have sufficient surface where they touch the housing. This significantly reduces the effective regulating surface in its initial position. Once there is enough outlet pressure, the housing moves and causes a sudden increase in the effective regulating surface. This causes a sudden increase of the opposing spring force which, in turn, further moves the plunger significantly and decreases the outlet pressure. When observing the outlet pressure curve of the regulators with this system, there are a slope and oscillations in the inlet pressure area near the pressure of regulation. This regulator, U.S. Pat. No. 4,474,207, also has five pieces and two accessories, problems and structures that have been solved by the present invention.
Two seals (o-rings) were added to correct the lateral movements or inclination of the plunger to assure that this piece maintains its coaxial position with respect to the fixed piston of the inlet piece. With this addition, the accuracy increased and the hysteresis decreased.
Eventually, if liquid should pass the first o-ring, it would be retained between the o-rings. The presence of this liquid would originate pressures which would prevent the normal movement of the cylindrical piece sideways and would therefore cause inaccuracy and an increase in the level of hysteresis. Also in the previous design, both planes of the closing between the inlet piece and the plunger were flat, therefore presenting the same problem mentioned before.
The present invention overcomes the problems of the prior art because the plunger slides over the first seal and a supportive element, but this does not work as a seal because it only supports the plunger. Because the plunger has two supporting points, it will always be in a coaxial position with respect to the piston over which it slides. Secondly, in the present invention the second support works as a support and not as a seal and does not retain liquids between the seal and the support because this space has been joined to the chamber formed between the intermediate cylindrical piece and the piston. This chamber is connected to the atmosphere to solve any problem of pressure build-up.
Concerning the flat surfaces of the closing planes, this problem was solved by the present invention by making both fronts conical. Thus, the closing is very efficient and the outlet pressure is leveled on both sides of the plunger which correspond to its thickness. When regulating the outlet pressure, the opposing spring force will always be constant. Also, in the regulator of the present invention, the point of support of the teeth of the cylindrical piece in the housing are small enough for their surface to be considered insignificant compared to the effective regulating surface, therefore not altering its work.
The present invention is a pressure regulating device for liquids consisting of three principal parts. The first part is an inlet through which the liquid enters and travels to the periphery of the device through internal tubes. This part includes a piston, which is fixed to it and over which slides a cylindrical plunger. This second part, the plunger, is closed at one end and has a toothed crown. The plunger slides over the piston fixed to the first part and by means of a sleeve, it opens and closes the internal conducts of the first part. This produces the regulation of the pressure of the outlet liquid. The third part, the housing, encloses the first and second parts. The third housing part forms a tube between itself and the second plunger part through which the liquid is led to the outlet of the regulator. The outlet is found on the third housing part.
The following accessory pieces complete the regulator of the present invention. A spring is situated between the inlet 1 and the intermediate or second part. The spring""s force maintains both parts separated and it opposes the force generated by the outlet pressure and the surface of the enclosed internal face of the second part. A seal hermetically closes the chamber that is formed between the piston fixed to the first part and to the second part. Finally, there is a supportive element, which together with the seal mentioned before, ensures that the second plunger, slides over the piston fixed to the inlet in a coaxial manner.